From "The Rough Guide to Vanth Subsector":

This large field of planetoids is so rich in dilithium that it sparkles like emeralds in the eternal night of space. But exploitation of these valuable minerals has proven quite difficult. The Vermilion Belt orbits a highly unstable star given to unpredictable novas, flares, and ion storms. And the Belt itself is inhabited by a large number of voracious Asteroid Worms.

As well as dilithium, the Vermilon Belt has also been shown to be a rich source of uraminium, glastane, Thrazarite, polarized phazinium, vulkinite, borosinium, and double-helixed plotholium.